The necessity for an efficient use of energy and for the availability of powerful sources of stored electric energy has led to the development of storage batteries having a high energy content. Such storage batteries are for example the high temperature sodium-sulfur batteries. In such batteries, the negative active mass is sodium and the positive active mass is liquid sulfur or liquid sodium polysulfide. The two substances are separated from one another by a solid electrolyte which is capable of conducting sodium ions. The normal operating temperature of such a battery is between 280.degree. and 350.degree. C.
The known substances which may be used as the solid electrolyte in the aforementioned sodium-sulfur batteries include crystalline ceramics, for example .beta.-alumina as well as non-porous, sodium ion-conducting glass. The conditions which an electrolyte glass must meet in sodium-sulfur batteries, are these:
1. A high conductivity for sodium ions. PA1 2. Corrosion resistance against other components of the battery, especially the sodium, the sulfur or the sodium polysulfide, and PA1 3. Workability. PA1 in which the ratio x/y lies between 0.52 and 0.92 and the ratio x/z lies between 2 and 20. It has been found that an electrolyte glass of the above composition exhibits the above listed qualities required in such a glass to a surprising degree.
In the early stages of development, a plurality of possible compositions for the glass electrolyte was cited, for example in U.S. Pat. No. 3,404,035 and U.S. Pat. No. 3,476,602. However, further development, for example as taught in U.S. Pat. No. 3,829,331, indicate that silicate glasses have insufficient corrosion resistance to sodium, sulfur, or sulfides and that borate glasses having a halogen component are more suitable for use as electrolytes.
A state of the art with respect to sodium-sulfur batteries with glass electrolytes is described in the article "The Dow Sodium-Sulfur Battery" published in the Proceedings of the 7th IECEC conference, San Diego, California, 1972 which also illustrates construction of such batteries. According to this article, the electrolyte is presented in the form of a large number of fibers or capillaries which have a specific resistivity of 5.times.10.sup.+5 Ohmns-cm at the operational temperature. This high resistivity permits only a very low current density with the result that a 40 Ampere-hour battery requires 27,000 capillaries. Some of the glasses cited in U.S. Pat. Nos. 3,404,035 and 3,476,602 are said to have lower specific resistivities, but these glasses are not usable in practice due to their insufficient corrosion resistance.